1. Field of the Invention
The present invention relates to a semiconductor laser device for optical communication, and more particularly to a semiconductor laser device in which a laser beam is radiated from a semiconductor laser placed in a hermetically-sealed package and is transmitted to an optical fiber through a window of the package.
2. Description of Related Art
In optical communication using an optical fiber, a semiconductor laser device is used. In this semiconductor laser device, a semiconductor laser (hereinafter, called a laser diode) is placed in a hermetically-sealed package, and a laser beam radiated from the semiconductor laser is transmitted to an optical fiber through a window of the package.
FIG. 16 is a view showing the configuration of a conventional semiconductor laser device. In FIG. 16, 101 indicates a laser diode configured to radiate a forward laser beam for optical communication and radiating a backward laser beam. 102 indicates a lens, arranged in front of the laser diode 101, for collimating the forward laser beam radiated from the laser diode 101. 103 indicates a package window through which the forward laser beam collimated in the lens 102 is output. The forward laser beam radiated from the laser diode 101 is transmitted through the package window 103 and is coupled to an optical fiber 105 through an optical interface unit 104. 106 indicates a photo diode, arranged in the rear of the laser diode 101, for receiving the backward laser beam radiated from the laser diode 101 and monitoring a light intensity of the backward laser beam to adjust a light intensity or wavelength of the forward laser beam according to the monitored light intensity of the backward laser beam. 107 indicates an LD carrier on which the laser diode 101 is mounted. 108 indicates a PD carrier on which the photo diode 106 is fixed. 109 indicates a base carrier on which the LD carrier 107 and the PD carrier 108 are mounted. 110 indicates a hermetically-sealed package in which the members of the conventional semiconductor laser device are arranged. The package window 103 is placed in a frontal side area of the hermetically-sealed package 110.
In the conventional semiconductor laser device having the above configuration, a control operation is performed to maintain intensity of the forward laser beam of the laser diode 101 to a constant value. In detail, because the intensity of the forward laser beam radiated from the laser diode 101 linearly changes with the intensity of the backward laser beam radiated from the laser diode 101, the backward laser beam radiated from the laser diode 101 is received in the photo diode 106, and a driving current supplied to the laser diode 101 is controlled so as to maintain a monitoring current generated in the photo diode 106. Therefore, the intensity of the forward laser beam of the laser diode 101 can be maintained to a constant value.
Also, a part of the forward laser beam radiated from the laser diode 101 is not transmitted through the package window 103 but is reflected on the package window 103 as a reflected laser beam. Therefore, in cases where the reflected laser beam is incident on the photo diode 106, the monitoring current generated in the photo diode 106 changes due to the reflected laser beam. In this case, even though the intensity of the backward laser beam received in the photo diode 106 is constant, the monitoring current is increased. Therefore, a problem has arisen that it is difficult to accurately control the driving current supplied to the laser diode 101. Also, in cases where the reflected laser beam is incident on a forward laser beam emitting point of the laser diode 101, laser beam radiation characteristics of the laser diode 101 are changed. Therefore, it is further difficult to accurately control the driving current supplied to the laser diode 101.
To prevent the reflected laser beam from being incident on the photo diode 106, a conventional semiconductor laser device has been disclosed in Published Unexamined Japanese Patent Application No. H7-162080 (1995). In this conventional semiconductor laser device, a light shielding member is soldered to an upper surface of the laser diode 101.
However, in cases where a manufacturing method of the direct soldering of the light shielding member to the upper surface of the laser diode 101 is adopted, a problem has arisen that the size and weight of the light shielding member is limited.
Also, it is required that a bonding wire is connected with the upper surface of the laser diode 101 to feed a driving current to the laser diode 101. However, in cases where the size of the light shielding member is enlarged, no bonding wire can be connected with the upper surface of the laser diode 101. Therefore, a conductive light shielding member is soldered to the upper surface of the laser diode 101 to supply a driving current to the laser diode 101 through the conductive light shielding member.
However, in the conventional semiconductor laser device for the optical communication, there is a case where the driving current is modulated to change the value of the driving current and is supplied to the laser diode 101 through a binding wire. Therefore, in cases where a modulated driving current is supplied to the laser diode 101 through the conductive light shielding member, an electric resistance of the conductive light shielding member for the modulated driving current is increased, and a problem has arisen that modulation characteristics of the modulated driving current are changed by the increased electric resistance of the conductive light shielding member.
Also, another conventional semiconductor laser device has been disclosed in the application. In this conventional semiconductor laser device, a lateral width of a light shielding member is shorter than that of the laser diode 101 so as to expose an upper surface of the laser diode 101 on a side of the light shielding member, and a bonding wire is directly attached to the upper surface of the laser diode 101 to supply a driving current to the laser diode 101. However, because the lateral width of the light shielding member is short, there is a probability that a part of the reflected laser beam passes through an area near to a side surface of the light shielding member so as to be incident on the photo diode 106.
An object of the present invention is to provide, with due consideration to the drawbacks of the conventional semiconductor laser device, a semiconductor laser device in which a reflected laser beam is reliably prevented from being received in a photo diode on condition that the supply of a driving current to a laser diode is not disturbed.
The object is achieved by the provision of a wavelength monitoring device of a first inventive idea. That is, the wavelength monitoring device comprises a semiconductor laser configured to radiate a forward laser beam and a backward laser beam, a photo detector configured to receive the backward laser beam radiated from the semiconductor laser, a lens configured to converge the forward laser beam radiated from the semiconductor laser, a window which transmits a most portion of the forward laser beam converged by the lens and on which the remaining portion of the forward laser beam is reflected as a reflected laser beam, a lens fixing member to which the lens is fixed, and a light shielding member, supported by the lens fixing member, for shielding the photo detector from the reflected laser beam.
In the above configuration, the light shielding member shields the photo detector from the reflected laser beam. Accordingly, the light shielding member can reliably prevent the reflected laser beam from being received in the photo detector without giving an adverse influence of the light shielding member on a driving current supplied to the semiconductor laser through a bonding wire.
The object is also achieved by the provision of a wavelength monitoring device of a second inventive idea. That is, the wavelength monitoring device comprises a semiconductor laser configured to radiate a forward laser beam and a backward laser beam, a photo detector configured to receive the backward laser beam radiated from the semiconductor laser, a window which transmits a most portion of the forward laser beam radiated from the semiconductor laser and on which the remaining portion of the forward laser beam is reflected as a reflected laser beam, a carrier on which the semiconductor laser is mounted, and a light shielding member, fixed to the carrier, for shielding the photo detector from the reflected laser beam.
In the above configuration, the light shielding member shields the photo detector from the reflected laser beam. Accordingly, the light shielding member can reliably prevent the reflected laser beam from being received in the photo detector without giving an adverse influence of the light shielding member on a driving current supplied to the semiconductor laser through a bonding wire.
The object is also achieved by the provision of a wavelength monitoring device of a third inventive idea. That is, the wavelength monitoring device comprises a semiconductor laser configured to radiate a forward laser beam and a backward laser beam, a carrier having a slot which is formed on a top surface, the semiconductor laser being arranged in the slot, a photo detector configured to receive the backward laser beam which is radiated from the semiconductor laser, a window which transmits a most portion of the forward laser beam radiated from the semiconductor laser and on which the remaining portion of the forward laser beam is reflected as a reflected laser beam, and a light shielding member, which is placed on the upper surface of the carrier so as to straddle the slot of the carrier, for shielding the photo detector from the reflected laser beam.
In the above configuration, because the light shielding member can be arbitrary placed in both a vertical direction and a direction of an optical axis of the semiconductor laser, the light shielding member can be placed at a position optimum to shield the photo detector from the reflected laser beam. Accordingly, the light shielding member can reliably prevent the reflected laser beam from being received in the photo detector without giving an adverse influence of the light shielding member on a driving current supplied to the semiconductor laser through a bonding wire.
The object is also achieved by the provision of a wavelength monitoring device of a fourth inventive idea. That is, the wavelength monitoring device comprises a semiconductor laser configured to radiate a forward laser beam and a backward laser beam, a photo detector configured to receive the backward laser beam radiated from the semiconductor laser, a lens configured to converge the forward laser beam radiated from the semiconductor laser, a window which transmits a most portion of the forward laser beam converged by the lens and on which the remaining portion of the forward laser beam is reflected as a reflected laser beam, a lens fixing member to which the lens is fixed, and a light shielding member which is supported by the lens fixing member and is formed in a U shape so as to cover an upper peripheral area of the semiconductor device.
In the above configuration, the reflected laser beam is transmitted through the lens to be converged at the upper peripheral area of the semiconductor device, and the light shielding member shields the photo detector from the reflected laser beam converged at the upper peripheral area of the semiconductor device. Accordingly, the light shielding member can reliably prevent the reflected laser beam from being received in the photo detector without giving an adverse influence of the light shielding member on a driving current supplied to the semiconductor laser through a bonding wire.
The object is also achieved by the provision of a wavelength monitoring device of a fifth inventive idea. That is, the wavelength monitoring device comprises a semiconductor laser configured to radiate a forward laser beam and a backward laser beam, a photo detector configured to receive the backward laser beam radiated from the semiconductor laser, a window which transmits a most portion of the forward laser beam radiated from the semiconductor laser and on which the remaining portion of the forward laser beam is reflected as a reflected laser beam, a carrier on which the semiconductor laser is mounted, and a light shielding member which is fixed to the carrier and is formed in a U shape so as to cover an upper peripheral area of the semiconductor device.
In the above configuration, the reflected laser beam is transmitted through the lens to be converged at the upper peripheral area of the semiconductor device, and the light shielding member shields the photo detector from the reflected laser beam converged at the upper peripheral area of the semiconductor device. Accordingly, the light shielding member can reliably prevent the reflected laser beam from being received in the photo detector without giving an adverse influence of the light shielding member on a driving current supplied to the semiconductor laser through a bonding wire.
The object is also achieved by the provision of a wavelength monitoring device of a sixth inventive idea. That is, the wavelength monitoring device comprises a semiconductor laser configured to radiate a forward laser beam and a backward laser beam, a photo detector configured to receive the backward laser beam radiated from the semiconductor laser, a window which transmits a most portion of the forward laser beam radiated from the semiconductor laser and on which the remaining portion of the forward laser beam is reflected as a reflected laser beam, a carrier on which the semiconductor laser is mounted, and a light shielding member which is fixed to the carrier and is formed in an L shape so as to cover an upper peripheral area of the semiconductor device.
In the above configuration, the reflected laser beam is transmitted through the lens to be converged at the upper peripheral area of the semiconductor device, and the light shielding member shields the photo detector from the reflected laser beam converged at the upper peripheral area of the semiconductor device. Accordingly, the light shielding member can reliably prevent the reflected laser beam from being received in the photo detector without giving an adverse influence of the light shielding member on a driving current supplied to the semiconductor laser through a bonding wire.
The object is also achieved by the provision of a wavelength monitoring device of a seventh inventive idea. That is, the wavelength monitoring device comprises a semiconductor laser configured to radiate a forward laser beam and a backward laser beam, a carrier having a slot which is formed on a top surface, the semiconductor laser being arranged in the slot, a photo detector configured to receive the backward laser beam which is radiated from the semiconductor laser, a window which transmits a most portion of the forward laser beam radiated from the semiconductor laser and on which the remaining portion of the forward laser beam is reflected as a reflected laser beam, and a light shielding member which is placed on the upper surface of the carrier so as to straddle the slot of the carrier and so as to cover an upper peripheral area of the semiconductor device.
In the above configuration, the reflected laser beam is transmitted through the lens to be converged at the upper peripheral area of the semiconductor device. Also, because the light shielding member can be arbitrary placed in both a vertical direction and a direction of an optical axis of the semiconductor laser, the light shielding member can be placed at the upper peripheral area of the semiconductor device optimum to shield the photo detector from the reflected laser beam. Accordingly, the light shielding member can reliably prevent the reflected laser beam from being received in the photo detector without giving an adverse influence of the light shielding member on a driving current supplied to the semiconductor laser through a bonding wire.
It is preferred in the wavelength monitoring devices of the first to seventh inventive ideas that the semiconductor laser is partially covered with the light shielding member, and the wavelength monitoring device further comprises a bonding wire which is connected with an upper surface of the semiconductor laser not covered with the light shielding member and through which an electric power is supplied to the semiconductor laser.
Therefore, the light shielding member can reliably prevent the reflected laser beam from being received in the photo detector without giving an adverse influence of the light shielding member on a driving current supplied to the semiconductor laser through the bonding wire.
It is also preferred that a backward end portion of the semiconductor laser is backwardly protruded from a backward surface of the light shielding member, and the bonding wire is connected with an upper surface of the backward end portion of the semiconductor laser.
Therefore, the bonding wire can be reliably connected with the upper surface of the backward end portion of the semiconductor laser.
It is also preferred in the wavelength monitoring devices of the first to seventh inventive ideas that a width of the light shielding member in a direction perpendicular to an optical axis of the semiconductor laser in a plane parallel to an upper surface of the semiconductor laser is longer than a width of the semiconductor laser in the direction.
Therefore, the light shielding member can reliably shield the photo detector from the reflected laser beam.
It is also preferred in the wavelength monitoring devices of the first to seventh inventive ideas that the window is inclined with respect to an optical axis of the semiconductor laser so as to return the reflected laser beam to a specific position placed at a peripheral area of the semiconductor laser, and the light shielding member is arranged at the specific position of the peripheral area of the semiconductor laser.
Therefore, the reflected laser beam does not return to the semiconductor laser, and the light shielding member reliably shield the photo detector from the reflected laser beam.
It is also preferred in the wavelength monitoring devices of the first to seventh inventive ideas that the window is inclined with respect to an optical axis of the semiconductor laser by placing a lower portion of the window near to the lens as compared with a position of an upper portion of the lens, and the light shielding member prevents the reflected laser beam from transmitting through an upper peripheral area of the semiconductor laser.
Therefore, the reflected laser beam is converged at the upper peripheral area of the semiconductor laser, and the light shielding member reliably shield the photo detector from the reflected laser beam.
It is also preferred in the wavelength monitoring devices of the first and second inventive ideas that the light shielding member is formed in a U shape and covers an upper peripheral area and side peripheral areas of the semiconductor laser.
Therefore, the light shielding member reliably shield the photo detector from the reflected laser beam.
It is also preferred in the wavelength monitoring device of the second inventive idea that the light shielding member is formed in an L shape so as to have both a horizontally-extending portion covering an upper peripheral area of the semiconductor laser and a foot portion fixed to the carrier.
Therefore, even though a member is additionally arranged on the carrier, the light shielding member can be arranged so as not to be in contact with the member, and the light shielding member reliably shield the photo detector from the reflected laser beam.
It is also preferred in the wavelength monitoring device of the second inventive idea that a member selected from a group of a circuit substrate for high frequency, an electric current feeding and modulating circuit, a thermister and a micro-strip line is placed on an upper surface of the carrier which is placed on an opposite side to the foot portion of the light shielding member formed in an L shape through the semiconductor laser.
Therefore, the light shielding member can be arranged so as not to be in contact with the member.
It is also preferred in the wavelength monitoring device of the second inventive idea that the light shielding member is arranged between the semiconductor laser and the photo detector, and the light shielding member has a through-hole through which the backward laser beam radiated from the semiconductor laser is transmitted to the photo detector.
Therefore, the light shielding member reliably shield the photo detector from the reflected laser beam.
It is also preferred in the wavelength monitoring devices of the first to seventh inventive ideas that the light shielding member partially surrounds peripheral areas of the semiconductor laser without making contact with the semiconductor laser.
Therefore, the light shielding member reliably shield the photo detector from the reflected laser beam converged at the peripheral areas of the semiconductor laser.
It is also preferred in the wavelength monitoring devices of the first to seventh inventive ideas that the wavelength monitoring device further comprises an optical element arranged between the semiconductor laser and the photo detector.
Therefore, even though a distance between the semiconductor laser and the photo detector is increased by the optical element so as to make a space in which the reflected laser beam is widely diverged, the light shielding member effectively shield the photo detector from the reflected laser beam.
It is also preferred in the wavelength monitoring devices of the first to seventh inventive ideas that the wavelength monitoring device further comprises a control circuit configured to adjust an intensity of the forward laser beam radiated from the semiconductor laser according to an intensity of the backward laser beam detected in the photo diode.
Therefore, the intensity of the forward laser beam can be reliably adjusted.
It is also preferred in the wavelength monitoring devices of the first, second, fourth, fifth and sixth inventive ideas that the light shielding member is a flat plate extending in a plane perpendicular to an optical axis of the semiconductor laser.
Therefore, the light shielding member reliably shield the photo detector from the reflected laser beam
It is also preferred in the wavelength monitoring devices of the first to seventh inventive ideas that the light shielding member is not soldered to the semiconductor laser.
Therefore, an adverse influence of the light shielding member is exerted on a driving current supplied to the semiconductor laser through a bonding wire.